The subject matter disclosed herein relates generally to overload relays, and, more particularly, to a modular overload assembly adapted to couple to a contactor assembly.
Overload relays are current sensitive relays that can be used to disconnect power from equipment when an overload or other sensed condition exists. They are normally used in conjunction with an electromechanical contactor, and are designed to protect an electric motor or other electronic devices.
In a typical installation, the contactor provides three contacts, one associated with each of up to three phases of power, that are closed by an electromagnetically operated contactor coil. The overload relay includes current sensing elements that are wired in series with the three phases passing through the contactor to the motor. In this way, the overload relay can monitor current flowing in the three phases through the contactor, and based on current magnitude and duration, may interrupt the current flow through the contactor coil circuit to open the contactor contacts when an overload occurs. For this purpose, the overload relay includes a contact or contacts that can be used to control the contactor coil and/or provide a signal indicating an overload or other sensed condition.
One difficulty associated with overload relays in general is the large number of catalog numbers that need to be manufactured and warehoused. Typically, an overload relay is designed for only a small current range, and possibly a fixed set of functional options. If you are a manufacturer, you want to offer a full product line, which means offering a large variety of overload relays that operate at their respective currents. If you are an integrator or an OEM using overload relays, this mean that you need to have available a large selection of overload relays for your application's needs. Attempts to accommodate overload relays to operate in a wider range of applications results in increased size, cost, and heat generation.
When modular components are used, the modules requires reliable electronic interconnection between the modules. One primary problem is to minimize or eliminate electrical contact wear caused by relative mechanical motion between modules. When connection points are not visible for a user, this presents an extra burden on minimizing relative motion between modules. An overload relay which is directly mounted to an electromechanical contactor further exacerbates this burden by subjecting the device to millions of shock-like operations.
Still other difficulties associated with overload relays include a lack of built in voltage sensing capabilities. In order to sense voltage, an add on module is required that increases the width of the overload relay, increases cost, and requires further wiring to be completed by the user. In addition, control wiring needs to be completed by the user when the overload relay is wired to a contactor.
There is a need, therefore, for a modular overload relay assembly that can sense voltage and still allow a significant reduction in catalog numbers while still providing a large array of product combinations. There is also a need for an easy yet reliable configuration for a user to mechanically and electrically connect modules in the field and connect an overload relay to a contactor.